fix #837 
the default blockscout image version does not work on my machine. 
so i added the blockscout_params for blockscout service. now user can
customize the image versions they want to use.
it contains two params:
```yaml
blockscout_params:
  # blockscout docker image to use
  # Defaults to the latest image
  image: "blockscout/blockscout:latest"
  # blockscout smart contract verifier image to use
  # Defaults to ghcr.io/blockscout/smart-contract-verifier:v1.9.0
  verif_image: "ghcr.io/blockscout/smart-contract-verifier:v1.9.0"
```

i already tested it on my machine and it worke well.

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Co-authored-by: Barnabas Busa <barnabas.busa@ethereum.org>
Co-authored-by: Barnabas Busa <busa.barnabas@gmail.com>